The objectives of this project are twofold: (1) Partial purification and characterization of the increased proteolytic activity associated with high metastatic potential mouse melanoma cells, and determination of its role in the production of metastasis. (2) Characterization of the cycle nucleotide system in mouse melanoma cells of low and high metastatic potential both in vivo and in vitro and attempts to suppress metastasis in vivo by manipulating the cyclic nucleotide system of high metastatic potential melanoma cells. The goals set for the second year of this project were as follows: Comparisons of intra- and extracellular proteolytic activity in F1, F5 and 510 cells using protamine sulfate as substrate. Initial characterization of the proteolytic activity, i.e., substrate specificity, trypsin-like or chymotrypsin-like activity. Continued studies on the cyclic nucleotide metabolism of F1, F5 and F10 cells with particular emphasis on the number of hormonal receptors for MSH and prostaglandin E1.